Pyroelectrical materials demonstrate the pyroelectric effect. In this connection, these materials react to temperature changes by building up an electrical voltage. This is particularly disadvantageous for components that are built up on pyroelectric substrates, for example, piezoelectric components or surface wave components. In this connection, such large voltages, i.e., field intensities, may build up between the electrically-conductive structures of these components, which have a more or less small size, and are applied directly on the pyroelectric substrate, that electrical sparkovers may occur between the small metal structures. As a result, the structures, and therefore the component, may be damaged or destroyed, unless suitable protective measures are taken.
Furthermore, the properties of the piezoelectric substrate material, and therefore also the component properties, may be irreversibly changed, or the component may actually become unusable, because of the high field intensities that occur. If the pyroelectrical voltages occur during operation of the component, the electrical fields or the sparkovers may trigger pulses between the electrically-conductive structures, which may result in incorrect signal processing in the electronic circuit.
Undesirable pyroelectrical voltages that are attributable to great changes in temperature occur particularly in the production of components with a pyroelectric substrate. A known means of preventing damage caused by pyroelectric charges is to provide ionization devices during production. By offering mobile charge carriers of a suitable amount and polarity in the ambient atmosphere of the pyroelectric substrate, the charges on the substrates, which are usually fixed in a specific location, may be compensated to a great extent. However, this is a technically complex method that is furthermore not suitable for all production processes. Also, a pyroelectric surface covered with electrically insulating or passivating layers may no longer be sufficiently discharged using ionization electrodes. Furthermore, the ionization electrodes are sensitive to various thin-layer methods and would also be damaged by the organic gas evolution that occurs in oven processes, for example.
From EP-A-0 785 620, it is known to protect components on pyroelectric substrates against damage caused by pyrodischarges, by means of conductive layers applied over the entire surface of the substrate, or under the component structures. A disadvantage in this connection is that the additional material layer may change the component properties in an unacceptable manner, and that the electroacoustic coupling or the spreading velocity of a surface wave is changed or actually attenuated.
Furthermore, it is possible to connect the metallic, electrically-conductive component structures conductively with one another, for example, by providing narrow metal strips that are structured to form a high-resistance connection, for example in a meander arrangement. However, these connections require a significant substrate area, which is counter to the increasing miniaturization of the components. Furthermore, because of their geometry, they are susceptible to electrical interruptions during the production process, particularly in the case of surface wave components, which may demonstrate a complicated arrangement and complicated wiring of several converter structures on a chip. It may be impossible, in some cases, to protect all the converters in this way, if there is not sufficient space available for the structures to be protected, and if the technologies used do not allow any crossing of printed conductors. The problem cannot always be solved even with additional bonded-wire contacts for connecting different electrically-conductive structures, and furthermore, this causes high costs.